This invention relates to a precision-wound rotor for a high speed dynamoelectric machine, and more particularly to a structure and a method for facilitating the manufacture of such a rotor.
Many dynamoelectric machines, including certain types of electric motors or generators, utilize a rotating member, which is known as a rotor, having a winding formed from layers of turns of wire wound about a rotor core of magnetic material. Rotors which provide superior performance and compact physical size can be produced by precision-winding the turns of wire about the rotor core.
In such precision-wound rotors, as shown in FIG. 1, the turns of wire 1-23 are precisely positioned within generally planar, overlapping layers 144,146,147 of the winding 118 in a side-by-side fashion with each turn in a given layer closely abutting an adjacent turn in that layer. The turns are preferably offset by one-half wire diameter in adjacent layers, so that each turn of wire will rest in a groove 148 formed between adjacent turns of wire in the preceding and any subsequent layers of the winding 118.
The precision-wound winding is generally contained in a slot 116 or channel of the rotor core 102. Ideally, as shown in FIG. 1, the winding 118 is formed in such a manner that the outer turns of wire 1,8,16,23 in the radially innermost and outermost layers 160,162, and the outer turns in alternating intermediate layers, bear simultaneously against a wall 132,134 of the slot 116 and/or one of more adjacent turns of wire in the winding 118, to form a densely packed structure.
In such a densely packed structure, the space occupied by the turns is minimized and remains highly consistent from one rotor to another, thereby allowing such precision-wound rotors to be physically smaller and more tightly toleranced than non-precision-wound rotors. Precision-wound rotors are also inherently more structurally self-supporting due to the interlocking nature of the turns within the slot 116, thereby allowing a precision wound rotor to operate safely at high rotational speed without fear of centrifugal forces causing the turns to shift, in contrast to non-precision-wound rotors in which shifting of the turns is known to occur.
Where cooling fluid is pumped through the winding 118, precision-winding provides superior heat transfer, thereby allowing wire size and/or coolant flow to safely be reduced without fear of the winding overheating. This improved heat transfer results from the turbulent fluid flow which occurs in the small interstices 156 which are formed between adjacent turns of the precision wound rotor. In non-precision-wound rotors, the interstices are larger, thereby causing laminar instead of turbulent fluid flow, which results in lower heat removal capability and the need for larger wire sizes and/or coolant flow rates in order to maintain acceptable temperatures in the winding. Commonly assigned U.S. Pat. Nos. 4,583,696 and 4,603,274 to Mosher are illustrative of precision-wound rotors as described above.
For precision-wound rotors having an odd number of layers of turns, as illustrated in FIG. 1, the tightly wound winding 118 supported by walls 132,134 of the slot 116 as described above, may be readily manufactured with minimal difficulty due to the fact that the first and last layers 160,162 can be configured to extend entirely across the width W2 of the slot 116 in the core 102. However, as illustrated in FIGS. 2 and 3 where the winding 118 includes an even number of layers having each turn nested in a groove 148 formed by turns in an adjacent layer as described above, either the innermost layer 160 or the outermost layer 162 of the turns will not extend entirely across the width W2 of the slot 116, and will thus not be fully supported by the slot walls 132,134.
Stated another way, for the desired nesting of turns to occur in adjacent layers of turns, the turns in one layer of each pair of adjacent layers of the winding 118 must be offset by one-half wire diameter from the turns in the other layer of the pair of layers. For a slot 116 having parallel walls 132,134, this means that if one member of the pair of layers has n turns of wire, the adjacent member of the pair of layers must have either n+1 or nxe2x88x921 turns. Therefore, if the slot 116 has a width W2 equal to (n+1)xc3x97(the wire diameter D), either the innermost 160 or outermost 162 layer of the winding 118 will have only n turns, and thus will not extend entirely across the slot 116, or be supported by the walls 132,134.
If the outermost layer 162 has only n turns, additional structure or winding retaining means may be required to preclude shifting of the turns as the result of centrifugal forces acting on the turns incident with rotation of the rotor. It would appear to be preferable, therefore, to have the innermost layer contain only n turns, as depicted in FIG. 3, since an overlying layer of n+1 turns, which extends entirely across the slot 116 will trap the innermost layer against the bottom surface 130 of the slot, thereby precluding movement. However, with the innermost layer 160 having only n turns, and not extending entirely across the slot width, some means of fixturing the innermost layer during fabrication of the winding must be provided to ensure that the subsequent layers having n+1 turns will fit properly within the slot width and simultaneously nest within the grooves between adjacent turns in the innermost layer of turns. Such fixturing increases the difficulty and cost of manufacturing the precision-wound rotor. The inconvenience and cost of providing such fixturing becomes even more acute with respect to repair or re-manufacturing of a damaged rotor in need of having the winding 118 replaced. Repair or re-manufacturing operations are often preferably carried out at repair centers or depots remote from the facility in which the rotor was originally manufactured. If special fixturing is required for precision winding, duplicate sets of such fixturing will need to be maintained at every remote repair or re-manufacturing facility. In many instances, the cost of maintaining and utilizing such duplicate fixturing at the remote sites will be so prohibitively high that damaged rotors will have to be shipped back to the initial manufacturing facility for repair, or worse yet, simply discarded and replaced with a new rotor, thus greatly increasing the cost of ownership of the dynamoelectric machine.
Accordingly, it is an object of my invention to provide a precision-wound rotor having an even number of layers of turns which is self-fixturing, and may thus be more readily manufactured at low cost without specialized fixturing or tooling. It is also an object of my invention to provide such a rotor in a form which may be readily repaired by re-winding the rotor at a remote repair facility or depot, without the use of specialized fixturing.
My invention accomplishes these objects in a precision-wound rotor through inclusion of a self-fixturing wire-guiding feature, such as a shoulder or a chamfer, in the corners of slots in the rotor core which contain the precision-wound winding.
Specifically, the precision-wound rotor of my invention includes a magnetic core having a slot therein for receipt of a winding having a first layer of n turns of wire and a second layer of n+1 turns of wire. The slot includes a generally planar bottom surface thereof, and sidewalls intersecting with the bottom surface to form corners of the slot. The sidewalls are disposed equidistant from a slot centerline bisecting and extending perpendicularly outward from the bottom surface of the slot. A self-fixturing wire-guiding feature is provided for centering a first and a second layer of the winding about the slot centerline within the slot in such a manner that when the first layer is formed by winding the turns of the first layer in a side-by-side fashion across the bottom surface of the slot, with each of the turns tightly abutting a radially outer surface of an adjacent turn in the first layer, each pair of adjacent turns in the first layer defines a groove extending parallel to the turns of wire for receipt therein of a turn of wire in the second layer of turns.
According to one aspect of my invention, the wire from which the turns of the winding are formed has a diameter D, and the self-fixturing wire-guiding feature includes a spacer at each corner of the slot having a width substantially equal to about one-half of the wire diameter D extending along the bottom surface of the slot, and a height extending along the sidewall of the slot substantially equal to about the wire diameter D.
According to another aspect of my invention, the wire used to form the turns of the winding has a diameter substantially equal to about D and the sidewalls are configured to define a width W. of the bottom surface of the slot which is substantially equal to about the number of turns n times the wire diameter D, and a second width W2 of the slot substantially equal to about (n+1) times D beginning at a distance substantially equal to about D along the sidewall from the corner of the slot.
In some embodiments of my invention, the self-fixturing wire-guiding feature of my invention is provided by configuring the corners of the slot itself to include a chamfer or a shoulder as defined above. In other embodiments of my invention, the self-fixturing wire-guiding feature is provided by a specially shaped slot liner which is inserted into the slot prior to precision winding of the turns therein.
The self-fixturing wire-guiding features of my invention, thus eliminate the need for special fixturing during either the initial manufacture or subsequent repair and rewinding of a precision-wound rotor. As a result, the cost of initially acquiring, and the long term cost associated with ownership of a dynamoelectric machine having a precision-wound rotor according to my invention are substantially reduced. Other objects, aspects, and advantages of my invention will become readily apparent upon consideration of the following drawings and detailed descriptions of preferred embodiments.